In practice, after a paper break, the web is threaded in stages through the papermaking machine by cutting a tail and threading the tail through the machine. Any part of this threading process that can be automated is advantageous because it reduces downtime associated with web breakage. The term tail refers to an edge piece cut into the traveling web by means of a cut into the web from the edge of the web and a continuous slit along the web which forms the "tail" or "edge piece" of the paper web. This tail may be blown or directed into the next portion of the paper making machine at which time the remainder of the web is severed widening the tail, so that the tail pulls the web through the next portion of the machine to be threaded. Typically the tail is anywhere from 10 to 20 centimeters in thickness compared to the remainder of the width of the web which can be in the order of 7 meters.
In the calendering section of a paper machine, a leader, or tail is cut upstream of the calender anywhere from 10-20 centimeters in width and threaded through the calender stack into nips formed by two-, or several successive rolls of the calender, at which point it emerges from a last nip formed by an upper "queen roll" and a lower "king roll". As the tail passes through the last nip, the tail follows the king roll and is removed from the king roll by a doctor blade that directs the paper web into a broke pit. Once the tail is threaded through the last nip in the calender, the tail cutter upstream of the calender widens the web to full web width which can be in the order of 7-10 meters.
It is at this stage that the tail cutter upstream of the calender is cutting a new slit into the web which now follows through all nips and emerges at the king roll as a fresh tail. This new tail must be severed, or "chopped" in its cross width for threading into the next section of the papermaking machine such as a reel, winder, coater, or possibly a dryer section.
While the use of waterjet cutting devices to cut a tail in a papermaking machine has been disclosed in U.S. Pat. No. 4,931,140 issued Jun. 5, 1990 to Peltola et al, this patent is primarily concerned with moving the water jet back and forth at a suitable rate to reduce wetting of the web supporting felt. There is no teaching associated with how to use such a waterjet cutting device in association with tail cutting in a calender section of a papermaking machine where the web passes or travels over rolls in the papermaking machine and must be removed from those rolls.
An automatic web threading apparatus for a calender section of a papermaking machine is disclosed in U.S. Pat. No. 4,904,344 issued Feb. 27, 1990 to Robert E. Peiffer. This patent teaches using a foil that moves into engagement with the edge of the web passing over the king roll downstream of the nip between the queen and king rolls. The doctor blade associated with the king roll includes an air nozzle that directs air up towards the underside of web. The air nozzle and the foil combine to cause the edge of the paper web to lift off the king roll. A support plate tray carries a knife that moves the knife blade forward into contact with the edge of the paper lifted off the king roll to cut a tail from the edge of the paper. The knife is withdrawn and the tail travels over the support plate to the next section of the paper making machine. While this patent discloses an automatic tail cutter and threading apparatus, the patent requires the movement of a foil into contact or close proximity with the web at the king roll, an air nozzle and movement of a cutting blade into the web portion lifted off the first or king roll.
U.S. Pat. No. 5,622,601 issued Apr. 22, 1997 to Adams et al discloses a combination doctor and waterjet cutting device fixedly located relative to each other on a platform that moves laterally of a roll to clip a tail edge and remove the tail edge from the roll. In this arrangement both the waterjet and doctor blade move into position with the roll. This arrangement, however, does not allow for a reverse cut should a new tail need to clipped as a result of improper threading of the clipped tail downstream.
It would be an advantage over the above discussed automatic web threading apparatus to provide an automatic tail cutting, severing and threading apparatus for use in a calender section of a papermaking machine that does not require movement of apparatus, such as a foil or doctor blade, into position to effect clipping of a tail in a web or removal of the clipped tail since these moving parts complicate the machine and consume time to be moved into place. The quicker the tail can be cut from the web, the less paper is wasted during the threading process.